Project Summary/Abstract Aging is a dominant risk factor for cardiovascular disease, the leading cause of death in the United States. Even in individuals without concomitant cardiovascular disease, aging results in progressive structural and functional decline of the hearts. Aging is associated with a decline in diastolic function, an increase in the prevalence of left ventricular hypertrophy, reduced cardiac reserve, and impaired myocardial performance. Decline in diastolic function is a hallmark of cardiac aging, and there is presently no treatment for diastolic failure (heart failure with preserved ejection fraction, HFpEF), which is especially prevalent in aged women. Although the phenotypes of cardiac aging are well-characterized, the molecular mechanisms of cardiac aging are not well established and no intervention has been developed to treat cardiac aging or HFpEF. Recently, our lab has shown that late-life rapamycin treatment of 10 weeks can reverse established murine cardiac aging, including a reversal of diastolic dysfunction. However, the mechanism of this protective effect is not well characterized. The objective of the proposed study is to determine how rapamycin reverses age- related diastolic dysfunction and define the signaling pathways that mediate the reversal. I hypothesize that rapamycin reverses age-related diastolic dysfunction by triggering improved cardiomyocyte calcium handling and beneficial ECM remodeling by inhibitions of both TORC1 and TORC2 signaling. To address this hypothesis, I will 1) determine the mechanisms by which rapamycin treatment rejuvenates cardiomyocytes to improve diastolic function in old hearts; 2) determine the mechanisms by which rapamycin treatment remodels extracellular matrix to improve diastolic function in old hearts; and 3) determine the contributions of TORC1 and TORC2 signaling on rapamycin rejuvenating benefits and define the downstream signaling pathways. In the mentored phase, I will receive trainings from my mentors and master the skills required for the proposed study. This award will facilitate my transition into an independent investigator in cardiac aging research. The results of study will lead to fundamental insights into key regulators of cardiac healthspan and help guide future translational studies of rapamycin treatment for HFpEF, a previously untreatable disease of aging.